Castlelost is a townland in County Westmeath, Ireland. It is located within the civil parish of Castlelost. The R446 road runs through the middle of the area, and a section of the R400 links the townland with the M6 motorway. Castlelost townland is bordered by Castlelost West and Clontytallon to the west, Derry to the north, Farthingstown and Oldtown to the south and Gortumly and Rahanine to the east.